Bioavailability 2 ,3,7,8-TCDD from contaminated

Umbreit TH, Hesse EJ, Gallo MA. 1986a. Differential bioavailability of TCDD from contaminated soils. Abstracts Am Chem Soc 191 47. 

Berg et al ( 4) reported that uptake of TCDD and other dioxins and furans from dietary fly ash was less than H% in rats, 3.7% in guinea pigs, and 2.4 % in hamsters. Kuehl et al ( ) showed a minimum of 37.5% uptake of TCDD from contaminated lake sediments into carp. In an aquarium study, Kuehl et al ( ) found a maximum bioavailability of 2.1% to fish. Silkworth et al ] ) demonstrated toxicity of soot from a PCB fire however, the extremely low levels of TCDD in these materials make it difficult to relate these results to bioavailability of dioxins. 

UMBREIT ET AL. Bioavailability of TCDD from Contaminated Soils... 

The bioavailability of TCDD from soils contaminated in the environment is an important determinant for risk assessment at TCDD contaminated sites. Literature reports indicate significant variation in bioavailability of TCDD from different sites. Soils from two of the major TCDD contaminated sites are compared for toxicity in guinea pigs and induction of aryl hydrocarbon hydroxylase (AHH) in rats. Times Beach, Missouri, soil is toxic and TCDD is highly bioavailable from this soil whereas Newark, New Jersey, soil is relatively non-toxic and has low bioavailability of TCDD. However, AHH induction in rats was approximately identical. These results confirm previous studies on bioavailability from these soils, and suggest that AHH induction may be an unreliable indicator of bioavailability. 

Examination of the literature regarding bioavailability of TCDD from environmental materials (Table I) reveals several important points. (1). Bioavailability of TCDD appears to be quite variable, depending on the site and material tested, and the species used as an assay system. (2). Laboratory contaminated samples yield different reactions than environmentally contaminated samples. It appears that TCDD added to soil in the laboratory is much more bioavailable, at least initially, than TCDD on materials contaminated in the environment. (3). Apparently the amount of time TCDD has been in contact with the substrate greatly affects its bioavailability and chemical extractablility. This effect may be a physiochemical ageing or a weathering phenomena. 

Poiger and Schlatter 2) reported a series of experiments on the absorption by animals of TCDD from various materials contaminated in the laboratory. The percentage of the TCDD dose (tritiated TCDD in ethanol) found in the liver of treated animals varied with the amount of time between dosing and assay, and the size of the dose of TCDD. They found that TCDD added to soil in the laboratory was about one quarter as bioavailable as the pure compound, and that this bioavailability was reduced (from 24% to 16%) by increasing the time of contact between soil and TCDD before dosing (from 24 hours to 8 days). They also reported that TCDD in a mixture with activated charcoal was only slightly bioavailable. 

McConnell et al (8) studied the bioavailability of TCDD from the dioxin contaminated soils at Times Beach, Missouri. They reported a bioavailability (based on toxicity data and aryl hydrocarbon hydroxylase induction) of approximately 60-85% from soil from Times Beach, Missouri. Lucier et al ( ) examined the same Missouri soils as reported by McConnell et al Using AHH induction in rat liver as a measure, they estimated that TCDD was about 25-50% bioavailable from these soils. These data demonstrated a clear dose response for TCDD toxicity and AHH induction from the contaminated soils. 

TCDD and other chlorinated dibenzo-J -di-oxins are released during the combustion of many polychlorophenols and also occur as contaminants in various chemicals such as the herbicide 2,4,5-trichlorophenoxyacetic acid. Most high-level exposure to 2,3,7,8-TCDD and other dioxins results from accidental releases or explosions in chemical plants or storage facilities for dioxin-containing chemicals. Because of the persistence of dioxin congeners in the environment and their potential for bioaccumulation, exposure may occur via the soil, air (especially when dioxins occur as combustion products), or water. When bound to components of the soil, the health hazard from 2,3,7,8-TCDD is reduced compared to ingestion of the pure compound. However, its bioavailability varies with the specific media in which it occurs. 

The results presented, and the previous reports confirmed by these results, demonstrate that soils from different TCDD contaminated sites have different toxicities and may represent quite different risks to human populations. The exact factors that influence the bioavailability of toxicants from soils remain to be elucidated. 

---